1. Field of the Invention
The present invention relates to a method and an apparatus of adjusting the tonal characteristics of a color or gray scale image and a graphic user interface for the same, and more particularly, to a method and an apparatus of adjusting the tonal characteristics of a color or gray scale original image and a graphic user interface where a minimum number of variables are used.
2. Description of the Related Art
In general, when a color or gray scale original image is input from an input device, such as a scanner or a multifunction peripheral, a user may vary chromatic characteristics or tonal characteristics of the original image before printing the original image using an output device, such as a printer or a multifunction peripheral. Because a printer driver or firmware of the printer only provides very simple options, such as a function to set a general sharpness of the image including text, graphics, or photographs, an additional graphic program, such as Adobe Photoshop or Corel Photopaint, is necessary for the user to change the chromatic characteristics or the tonal characteristics of the original image to the extent to which the user desires.
Such a graphic program provides various functions for adjusting the chromatic characteristics or the tonal characteristics of the original image, including a level function and a curve function. According to the level function, a distribution of brightness of portions of the original image is represented by a histogram. Thereafter, portions of the original image are classified into a shadow region, a middle tone region, and a highlighted region. A clear image is obtained by adjusting the brightness and a contrast of the original image taking the classified region into consideration. Therefore, the level function enables the user to adjust the brightness and the contrast of the original image more precisely than a brightness/contrast function for adjusting the overall brightness and contrast of the original image.
The curve function helps the user adjust the chromatic characteristics or tonal characteristics of the original image even more precisely than the level function. According to the curve function, the brightness and the contrast of the image are freely adjusted by arbitrarily changing a color gamma curve so that the brightness and the contrast of the shadow region, the middle tone region, and the highlighted region can be individually adjusted. In addition, the curve function enables the brightness and the contrast of the original image to be adjusted on a channel basis and the color of the original image to be adjusted directly on the image. The user can change a shape of a color gamma curve provided in a graphic user interface for the curve function by dragging the color gamma curve toward a predetermined direction using a pointing device, such as a mouse, or drawing a new color gamma curve having a desired form using a pen tool, and by doing so, the user can adjust the brightness and the contrast of the original image.
However, in general, the graphic user interface provided by the conventional graphic program includes many variables necessary to change the shape of the color gamma curve. The shape of the color gamma curve responds to the manipulation of the pointing device so sensitively that even an expert user as well as an inexperienced user may have difficulty in using the pointing device to change the shape of the color gamma curve. In addition, in the conventional method of adjusting the color or the gray scale of the image, because an additional graphic program is necessary to adjust the chromatic characteristics or the tonal characteristics of the original image, frequently adjusting the chromatic characteristics or the tonal characteristics causes an inconvenience to the user and it is difficult to adjust the chromatic characteristics or the tonal characteristics at a high speed.
Furthermore, U.S. Pat. No. 5,898,436 discloses a graphical user interface for digital image editing, in which the chromatic adjustments to an overall color balance of the image are presented on one screen and the tonal adjustments are presented on another screen. Each adjustment is displayed as a pair of preview images which respectively show the effect of the associated variable in a real time. U.S. Pat. No. 5,424,754 discloses a method and apparatus for color processing of the image displayed on a display device in a computer controlled display system, in which a display screen includes a window displaying a user image, a window displaying a reference image, a window for analog color controls and a window displaying variants. The user can modify the color of the image displayed on the display device easily and conveniently using either the analog color controls or the variants.